16 February, 2017, 10:51:47 PM

Hi guys.I hope I put this in the right forum.

First, here's the video, and then afterwards I'll elaborate. The point in question is by David Robinson at 11:46, but this is a continuation of an answer to a question that was asked at 5:23 and then elaborated on by Robinson at 8:47

So, my question is:Is what David Robinson claiming true or false, and if what he is claiming is true, is it also audible?

hopefully you can tell me something along the lines of:"yes, what the person says in the video is completely correct, and that phase shift is always audible on all CDs", or "no, his claim is completely false and it's never audible under any legitimate circumstances, unless a CD is intentionally made to be like that, but nobody would do that when releasing music", or "his claim of audibility only applies when something has gone wrong when making a CD, so under legitimate circumstances where nothing has gone wrong, there is neither any 'drift' in phase above 1 kHz, and nor can there be any audible effect, since there is no issue", or "in most cases, phase on CDs doesn't deviate to an extent that is worth worrying about" or another more fitting description.

It's also worth noting that David Robinson actually says "in the beginning", implying that it might be different now, but he still seems to be a CD hater.

I am aware that this topic may very easily go off-topic, so hopefully we can leave aside all the other claims made in the video, about 192 kHz sampling rates being audibly superior to 44.1 kHz ones, as I believe that's just another case of them not understanding the Nyquist theorem, and they haven't done any blind tests, and hopefully we can also leave out the claim that PCM and DSD sounds notably different, and that a recording of a vinyl disc will sound different than the vinyl disc itself, as the converter will leave it's sound imprint on the recording. While strictly speaking the latter might be true, then I like to think that most properly constructed converters nowadays are extremely close to 100 % transparancy and certainly transparent within audibility.

Last Edit: 17 February, 2017, 01:20:25 PM by kode54

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

That panel would likely not accept the results of a double-blind/ABX test anyway. The fact they claim audible differences that couldn't be proven in an ABX test is also expected. The explanation of phase shift caused by PCM sampling is complete nonsense. They presume vinyl/analog sound "better" because it doesn't suffer from that nasty digital phase shift problem. Except...they clearly have never bothered to look at the phase response, or square wave response of an analog tape recorder, or that tape cut to vinyl. Spoiler: Yes, it's different than PCM, No, it's not better than PCM.

The explanation of phase shift caused by PCM sampling is complete nonsense.

I think this type of misinformation happens because a lot of people think PCM audio works in discrete 'ticks', and that if the ratio between sampling rate and frequency becomes too low, you don't have enough "temporal resolution" to fully capture the sound wave.

It's all based on a gross misunderstanding of the Nyquist-Shannon sampling theorem.

I would love to play back a format that actually worked like that to these people, just to see their absolutely horrified expressions.

But I don't really understand this, so hopefully you can tell me something along the lines of:"yes, what the person says in the video is completely correct, and that phase shift is always audible on all CDs", or "no, his claim is completely false and it's never audible under any legitimate circumstances, unless a CD is intentionally made to be like that, but nobody would do that when releasing music", or "his claim of audibility only applies when something has gone wrong when making a CD, so under legitimate circumstances where nothing has gone wrong, there is neither any 'drift' in phase above 1 kHz, and nor can there be any audible effect, since there is no issue", or "in most cases, phase on CDs doesn't deviate to an extent that is worth worrying about" or another more fitting description.

And the right answer is:

...there is neither any 'drift' in phase above 1 kHz, and nor can there be any audible effect, since there is no issue...

For example, consider a modern converter that is designed to be Linear Phase, which is to say it has a phase versus frequency response that is practically the same as that of an ideal delay over the entire audible range.

These guys were as aware of the phase response of analog tape or vinyl, or microphones, or speakers or the general run of high quality studio gear that is in general use, they'd "Have a cow". Then there is the slight matter of the fact that the human ear does not perceive phase changes applied to both channels equally above about 1 KHz. There's no process in place to do so - the ear functions like a spectrum analyzer without any way to determine or pass on phase response. Finally, their claim that DSD is somehow free of these problems is yet another fantasy.

But I don't really understand this, so hopefully you can tell me something along the lines of:"yes, what the person says in the video is completely correct, and that phase shift is always audible on all CDs", or "no, his claim is completely false and it's never audible under any legitimate circumstances, unless a CD is intentionally made to be like that, but nobody would do that when releasing music", or "his claim of audibility only applies when something has gone wrong when making a CD, so under legitimate circumstances where nothing has gone wrong, there is neither any 'drift' in phase above 1 kHz, and nor can there be any audible effect, since there is no issue", or "in most cases, phase on CDs doesn't deviate to an extent that is worth worrying about" or another more fitting description.

And the right answer is:

...there is neither any 'drift' in phase above 1 kHz, and nor can there be any audible effect, since there is no issue...

For example, consider a modern converter that is designed to be Linear Phase, which is to say it has a phase versus frequency response that is practically the same as that of an ideal delay over the entire audible range.

These guys were as aware of the phase response of analog tape or vinyl, or microphones, or speakers or the general run of high quality studio gear that is in general use, they'd "Have a cow". Then there is the slight matter of the fact that the human ear does not perceive phase changes applied to both channels equally above about 1 KHz. There's no process in place to do so - the ear functions like a spectrum analyzer without any way to determine or pass on phase response. Finally, their claim that DSD is somehow free of these problems is yet another fantasy.

Thanks for your help :-).So just to make sure I understand you correctly, although you were pretty clear about it:What David Robinson is saying is basically just made up? There's no phase drift/skewing?

I've seen people make up these things before, but as I didn't know much about this issue it sounded "scientifically enough" to make me doubt whether it was true or false. I've also looked at Ethan Winer's "Audio Myths" video, and in there he plays clips with phase shift at certain frequencies with no audible effect.Robinson did also say "in the beginning", so I figured maybe this was before linear phase filters became common, which I think was in the early 90s (but I could be mistaken).

Last Edit: 17 February, 2017, 12:00:53 PM by board

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

The statement that, with 44.1kHz sampling, a 20 Hz sine is well sampled, but above 10k the phase is "totally random", sounds to me like a "grid snapping" mental model, where you imagine that sine wave peaks must be snapped to the nearest sample point. e.g. at the Nyquist frequency of 22.050kHz, you would imagine that there is only one possible sine wave phase.

This is incorrect, though. I suggest watching Monty's "Digital Show and Tell" video, but in particular the part at 20:55 addresses this idea: https://xiph.org/video/vid2.shtml

I would be happy to hear more comments about the phase issue in particular (instead of sample rates etc.) :-).

JJ pointed me to some of his papers available publicly, and I think I might finally understand those points in his papers filtutv1 and src1_9_16:

Quote

“Linear Phase” (constant delay)- If a filter has a constant delay, the phase shift of the filter will be t*w, where t is the time delay, and w the natural frequency (2 pi f).* This means that a delay can exhibit enormous phase shift.* This phase shift, however, is ONLY delay.

Quote

* In most cases, a symmetric FIR (convolutional) filter is used. This kind of filter has a fixed (constant) delay over all frequencies, which means* It has a phase shift, relative to the input, of 2*pi*f*t, where f is the frequency of interest, and t is the time delay. This “linear phase” means that the signal is purely delayed, all frequencies arrive at the same instant.* It has a substantial amount of energy before the middle (main lobe) of the filter, being symmetric.* If it’s poorly designed, or is too short, you can get pre-echo. *Oddly, that doesn’t happen if it’s not too short. *That’s another story* This kind of filter design accounts for most filters in use

So, if I understand this correctly (and I might not), then the phase skewing that David Robinson talks about can only happen in other types of filters than linear phase filters.

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

This sort of phase issue "can" happen with any sampling frequency not perfectly factoring against the sample rate of components of the signal. The thing is, due to how signal reconstruction works, this does not matter.

This sort of phase issue "can" happen with any sampling frequency not perfectly factoring against the sample rate of components of the signal. The thing is, due to how signal reconstruction works, this does not matter.

I don't think so. I've never seen this happen, and I've looked for it. Please provide an independent reliable reference or a test sample.

There are some odd effects such as those where quantization distortion can be zero with some precondidtions including sample rate being a strict multiple of the signal frequency, but that is amplitude distortion, not phase distoriton. Also, if your signal frequency is within a few Hz of the Nyquist frequency, things can get strange, but again that is a very special case.

I would be happy to hear more comments about the phase issue in particular (instead of sample rates etc.) :-).

JJ pointed me to some of his papers available publicly, and I think I might finally understand those points in his papers filtutv1 and src1_9_16:

Quote

“Linear Phase” (constant delay)- If a filter has a constant delay, the phase shift of the filter will be t*w, where t is the time delay, and w the natural frequency (2 pi f).* This means that a delay can exhibit enormous phase shift.* This phase shift, however, is ONLY delay.

Quote

* In most cases, a symmetric FIR (convolutional) filter is used. This kind of filter has a fixed (constant) delay over all frequencies, which means* It has a phase shift, relative to the input, of 2*pi*f*t, where f is the frequency of interest, and t is the time delay. This “linear phase” means that the signal is purely delayed, all frequencies arrive at the same instant.* It has a substantial amount of energy before the middle (main lobe) of the filter, being symmetric.* If it’s poorly designed, or is too short, you can get pre-echo. *Oddly, that doesn’t happen if it’s not too short. *That’s another story* This kind of filter design accounts for most filters in use

So, if I understand this correctly (and I might not), then the phase skewing that David Robinson talks about can only happen in other types of filters than linear phase filters.

True.

If the phase distortion due to time delay were an audible problem duing music playback, then all forms of media, not just digital would be greatly affected because we listen to recordings minutes to decades after the live performance, and the phase shift due to delay ranges from astronomical to even a whole lot bigger.

Furthermore I got the impression that the speaker was referring to a phase shift that wanders around, while the phase shift due to the usual run of digital filters is fixed in place, rock solid. This contrasts with analog media, where the phase shift (and amplitude response) wanders around, often fairly audibly.

May he's objecting to digital's inherent constant phase shift as opposed to his preferred analog media phase shift that wanders around. And wander around, analog media does. It is not unusual for there to be 1 dB and greater variations within the audible range with both vinyl and analog tape playback.

Probably quantization effects, then. Not lining up with the frequency of the waveform, it can result in sample points appearing to be some sort of gibberish, until you do something like intelligently plot a curve between the points, like a reconstruction filter would.

Don't mind me, I only have a rudimentary understanding of this stuff, and have zero college education to boot. I pick up bits and bobs as I crawl the web and read people's code, and maybe even learn something!

I did manage to sort of guess an algorithm that turned out to be really close to what Paulstretch does, though. I guess I'm not totally out of touch.

I would be happy to hear more comments about the phase issue in particular (instead of sample rates etc.) :-).

JJ pointed me to some of his papers available publicly, and I think I might finally understand those points in his papers filtutv1 and src1_9_16:

Quote

“Linear Phase” (constant delay)- If a filter has a constant delay, the phase shift of the filter will be t*w, where t is the time delay, and w the natural frequency (2 pi f).* This means that a delay can exhibit enormous phase shift.* This phase shift, however, is ONLY delay.

Quote

* In most cases, a symmetric FIR (convolutional) filter is used. This kind of filter has a fixed (constant) delay over all frequencies, which means* It has a phase shift, relative to the input, of 2*pi*f*t, where f is the frequency of interest, and t is the time delay. This “linear phase” means that the signal is purely delayed, all frequencies arrive at the same instant.* It has a substantial amount of energy before the middle (main lobe) of the filter, being symmetric.* If it’s poorly designed, or is too short, you can get pre-echo. *Oddly, that doesn’t happen if it’s not too short. *That’s another story* This kind of filter design accounts for most filters in use

So, if I understand this correctly (and I might not), then the phase skewing that David Robinson talks about can only happen in other types of filters than linear phase filters.

True.

If the phase distortion due to time delay were an audible problem duing music playback, then all forms of media, not just digital would be greatly affected because we listen to recordings minutes to decades after the live performance, and the phase shift due to delay ranges from astronomical to even a whole lot bigger.

Furthermore I got the impression that the speaker was referring to a phase shift that wanders around, while the phase shift due to the usual run of digital filters is fixed in place, rock solid. This contrasts with analog media, where the phase shift (and amplitude response) wanders around, often fairly audibly.

May he's objecting to digital's inherent constant phase shift as opposed to his preferred analog media phase shift that wanders around. And wander around, analog media does. It is not unusual for there to be 1 dB and greater variations within the audible range with both vinyl and analog tape playback.

So, I just want to be competely sure I understand what both you, Arny, and the rest of you guys are saying:On digital medias, there IS a phase shift, but it's never audible. And the phase shift is constant, so therefore there is no audible effect, as the phase shift manifests purely as a delay. Is that correct?

On analogue medias, there is even more phase shift, and it's not constant and doesn't manifest itself as a delay, so it can be audible. Is that also correct?Are you also saying that on analogue medias, the phase shift varies from left to right channel, which is when phase shift actually becomes audible, and to some, like David Robinson, this phasing effect actually sounds pleasing, whereas the lack of audible phase shift, sounds "flat" to his ears.

So, David Robinson's claim was partly true, partly false...?

I'm also partly asking about this, as Michael Fremer bascially SCREAMED at me a few months ago on Youtube that vinyl has better phase resonse than CDs (as well as screaming that CDs have never been more transparent than, or as transparent as, vinyl + vinyl has wider bandwidth, as it can go to 30 kHz, but of course I do know that the claim of transparency is bullshit, and the claim of bandwidth is mosltly irrelevant, and vinyl rarely goes above 20 kHz except for distortion in the form of harmonics).

Last Edit: 22 February, 2017, 12:38:26 PM by board

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

So, I just want to be competely sure I understand what both you, Arny, and the rest of you guys are saying:On digital medias, there IS a phase shift, but it's never audible.

Given the really small phase shifts that we can now measure reliably and accurately, there is always some measurable phase shift.

However, in common kinds of digital audio gear, which is generally very good, well designed, and well made, there are no reliably audible artifacts while playing normal audio such as music, dialog, and dramatic sound effects.

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And the phase shift is constant,

No, it takes certain combinations of phase shift versus frequency to obtain linear phase. zero phase shift at all frequencies is one of them, but it is impossible in the real world except for trivial cases.

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... so therefore, there is no audible effect, as the phase shift manifests purely as a delay. Is that correct?

Yes, designing a linear phase filter with no audible effects is very doable. It could be an undergraduate class project in EE.

Designing linear phase 44.1 KHz and above sample rate reconstruction filters is a generally solved problem. For example there are at least two software products, one pretty expensive and one a freebie that will grind out the parameters for building an appropriate filter if you tell it what you want; This is known as a Cookbook design problem.

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On analogue medias, there is even more phase shift, and it's not constant and doesn't manifest itself as a delay, so it can be audible. Is that also correct?

Yes. One of the big systematic lies in high-end audio is publicly obsessing over certain performance attributes of digital, ignoring the fact that they are so well solved in the digital domain as to not be audible problems, and simply not mentioning that they were never that well solved in the analog domain, and are often very audible there. Two that come to mind quickly is jitter and phase shift.

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Are you also saying that on analogue medias, the phase shift varies from left to right channel, which is when phase shift actually becomes audible,

Having differing phase shifts in the two stereo channels vastly ups the odds of hearing it reliably as compared to having the identical phase shift in both channels. Having the phase shift vary pretty quickly with time makes it more audible, too. Combining it with concurrent variations in amplitude response increases the audibility as well. All of this is inherent and was never solved with analog media. They are inherent, and there is not much that can be done about it, except sometimes at great expense (FM recording) or by cutting to the chase and going to digital. By inherent I mean they are due to things like the geometry of LP grooves, cartridge armatures, analog tape heads, and turntable arms. You make them out of Unobtainium using those of Santa's Elves who have PhDs and who are also journeyman watchmakers, in a secret lab in Never-Never land, and the problems will still be there.

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and to some, like David Robinson, this phasing effect actually sounds pleasing, whereas the lack of audible phase shift, sounds "flat" to his ears.

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So, David Robinson's claim was partly true, partly false...?

I'm also partly asking about this, as Michael Fremer bascially SCREAMED at me a few months ago on Youtube that vinyl has better phase resonse than CDs (as well as screaming that CDs have never been more transparent than, or as transparent as, vinyl + vinyl has wider bandwidth, as it can go to 30 kHz, but of course I do know that the claim of transparency is bullshit, and the claim of bandwidth is mosltly irrelevant, and vinyl rarely goes above 20 kHz except for distortion in the form of harmonics).

Human nature being what it is, adding the sound of a Troll gargling with pi$$ mouthwash to every recording may be someone's preference, but it isn't mine. Probably not yours, either.

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Michael Fremer bascially SCREAMED at me a few months ago on Youtube...

Lucky me, he did it to me live and in person just before the 2005 Stereophile debate between John Atkinson and I. Somehow I recovered, I hope you do to, if you have not already done so... ;-)

Michael Fremer bascially SCREAMED at me a few months ago on Youtube...

Lucky me, he did it to me live and in person just before the 2005 Stereophile debate between John Atkinson and I. Somehow I recovered, I hope you do to, if you have not already done so... ;-)

Fremer also added on Youtube that his friends call him friendly and agreeable, but that's not how he comes across online at all, where he often has CAPS LOCK on AUTO and calls everybody morons if they simply present facts or voices their opinions, if any of those two go against his "all analogue medias are technically superior to digital".

Two more things:Arny, do you know if other types of digital filters, for instance minimum phase filters or the filterless non-oversampling DACs, have audible phase shift?

And lastly, here's a quote from a different website. I tried what this person suggested with several CDs. With many CDs I couldn't hear any difference, but with some I actually heard a big difference (and no, not like a $2000 power cord difference, but a real, immediately noticeable difference). If any of you happen to have the "About a boy" soundtrack by Badly Drawn Boy (or you could download and burn a CD-R, or get it from the library) that was the one where I heard the biggest difference, but I heard differences with other albums as well. I connected the speaker wires as red to red and black to black on my speakers, and black to red and red to black on my amp when doing this. On a different website, someone claimed that 92 % of CDs and CD players inverted the polarity, and he listed many albums where this was the case.If you're able to try this out, what do you think of this? I've tried hitting the "switch polarity" in Wavelab, and there was no audible difference.

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The answer to this age-old (well, the age of the first CD player anyway) argument among audiophiles is far more simple than the above explanation.

I’ve worked on (repair and restoration of) high-end audio equipment for years now. The reason vinyl is perceived as “better” than CD does indeed lie in the DAC, but the reasons listed above are minor compared to the real issue: The inversion of the polarity of the signal.

Some people mistakenly call this “phase inversion”, but that is an argument for another time. Unless someone makes a mistake installing the cartridge, turntables do not invert the polarity of the signal. As long as the rest of the amplifier/speaker combination is set up or built correctly, the signal is presented in the correct, natural polarity.

I have yet to run across ANY CD player/DAC that DIDN’T invert the polarity of the signal, even the $12,000 Sonic Frontiers CD player I changed the laser in once. I don’t know why this is, unless the red book specifications did it to limit the dynamic range of CD playback. You see, back then it was a common mistake for people to turn the volume up too far, because once they hit “play”, they were expecting to hear a little bit of the “hiss” of a tape or (cheap) high-gain phono preamp.

Anyhow, in defense of that Sonic Frontiers player, and a few nicer other machines as well, there is a “polarity invert” button, which in most cases corrects the polarity of the signal. Once the sound is presented to you in the correct polarity from the CD player, there is basically no perceivable difference. We’ve tested it many times, with turntables and CD players ranging from $50 to $22,000. Always the same results.

Before you call me crazy (something I will not deny actually), try this simple test: Listen to a recording using anything you like for a source. Then, immediately after, switch your speaker connectors to be “backwards”, i.e. + to – and – to +. You will most likely find that if you are using a CD player (or an iPod or computer, they all tend to invert polarity), the sound will be MUCH improved, and if you are listening to vinyl, the sound will get MUCH worse. If you find the opposite to be true, your system may have been inverting from the very beginning.

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

I made a typo in my post, although not related to what you're saying. In Wavelab it was "invert phase", not "switch polarity".Nevertheless, the whole polarity thing I consider complete bullshit as well - which is why I was so surprised to hear those big differences with certain CDs.On my phono preamp I have a polarity inversion switch, which doesn't have any audible effect.But if possible, please try out that experiment I mentioned :-).As far as I know my speakers don't have problems.

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

Funny thing, JBL used to label their speaker terminals backwards for decades, ie. a positive impulse at the black terminal would make the speaker cone move forwards. This was opposite to just about every other speaker maker in the world. And no one noticed, unless they were setting up a system with multiple speakers and needed to match the polarity and phase. I guarantee you that no home users actually noticed anything out of the ordinary.

The Chromecast Audio also inverts the signal, as do a lot of other devices. It seems to be almost random, and no one cares. Well, no one except obsessive audiophiles ;-)

Funny thing, JBL used to label their speaker terminals backwards for decades, ie. a positive impulse at the black terminal would make the speaker cone move forwards. This was opposite to just about every other speaker maker in the world. And no one noticed, unless they were setting up a system with multiple speakers and needed to match the polarity and phase. I guarantee you that no home users actually noticed anything out of the ordinary.

The Chromecast Audio also inverts the signal, as do a lot of other devices. It seems to be almost random, and no one cares. Well, no one except obsessive audiophiles ;-)

I agree with this - which is also why I was surprised to actually hear a difference in that test with SOME CDs. Many CDs showed no difference at all. So if you keep trying this, maybe you will hear a difference eventually, although I am aware that you might not do this as you clearly find it pointless :-).

"What is asserted without evidence can be dismissed without evidence"- Christopher Hitchens"It is always more difficult to fight against faith than against knowledge"- Sam Harris

I agree with this - which is also why I was surprised to actually hear a difference in that test with SOME CDs. Many CDs showed no difference at all. So if you keep trying this, maybe you will hear a difference eventually, although I am aware that you might not do this as you clearly find it pointless :-).